In wireless communication devices, radio frequency (RF) power amplifiers (PAs) are often used to provide transmit signals at increased power levels needed for operation within a communication system. For example, cellular telephone devices use PAs to transmit signals at power levels needed to communicate effectively with cellular base stations. In addition, these transmit power levels must often be regulated by the communication device. In prior communication devices, an RF coupler has been used to split off a proportional part of the transmit output signal so that the transmit output power can be monitored by the system.
FIG. 1 (Prior Art) is a block diagram for an embodiment 100 including an RF coupler 102 and power amplifier (PA) integrated circuit 104 for transmission of signals in a wireless communication system. As depicted, the PA integrated circuit 104 receives a transmit signal 114 from external circuitry, for example, from a transceiver or baseband processor integrated circuit. The PA integrated circuit 104 can also receive a transmit power (PWR) control signal 115 from this external circuitry. In operation, the PA integrated circuit 104 provides an amplified transmit signal on signal line 110 to a radio frequency (RF) coupler 102. The RF coupler 102 receives this amplified transmit signal and then outputs an RF transmit (TX) signal on signal line 112 to antenna switch (SW) circuitry 117 through a duplexer 106. The antenna switch (SW) circuitry 117 is coupled to antenna 121. For a transceiver embodiment, the antenna 121 can be used to send and receive RF signals, and the antenna switch circuitry 117 can provide these signals to and from the duplexer 106. In addition to receiving the transmit (TX) signal on signal line 112, the duplexer 106 can also output a receive (RX) signal on signal line 120. And this receive (RX) signal 120, for example, can be provided to other external circuitry, such as a transceiver or baseband processor integrated circuit, if desired.
As indicated above, the RF coupler 102 can be used in the embodiment 100 to provide an RF transmit (TX) power indicator signal to external circuitry, such as a transceiver or baseband processor integrated circuit. The RF coupler 102 has a transmit input connection port 132 and a transmit output connection port 134 that are connected to signal lines 110 and 112, respectively. The incoming amplified transmit signal on signal line 110 passes through input connection port 132 and output connection port 134 and is provided to the duplexer 106 as the transmit (TX) signal on signal line 112. The RF coupler 102 also includes a secondary signal line that is electro-magnetically coupled to the transmit signal line such that the signal on the coupled port 136 provides power proportional to the transmit forward power wave of the RF signal passing through ports 132 and 134, and such that the signal on the isolated port 138 provides power proportional to the reverse transmit power wave of the RF signal passing through ports 132 and 134. The RF forward power indicator signal generated on the output signal line 116 can be used as an RF transmit (TX) power indicator signal. For example, this RF transmit (TX) power indicator signal can be used by external circuitry to determine the transmit power being provided by the PA integrated circuit 104 and then to adjust the transmit (TX) power control signal 115 in order to achieve the desired transmit power to the antenna 121. It is noted that the output ports 136 and 138 for the RF coupler 102 can be terminated to ground using resistors (R), as shown, and these resistors (R) can be 50 ohm termination resistors. It is further noted that the termination of the output ports 136 and 138 can also be implemented through other connections to terminated components, if desired.
In addition to controlling transmit output power, communication devices often also require certain levels of electrostatic discharge (ESD) protection. As such, communication devices typically require certain levels of ESD protection to be provided by the circuitry used within the communication device, such as power amplifiers and RF couplers used in the communication device solution. It is often desirable and required, therefore, for the PA integrated circuit 104 and/or the RF coupler 102 to meet certain ESD requirements within the embodiment 100. For example, integrated circuits are often required to meet a 2 kV human body ESD model for static discharges. It is further noted that ESD events are typically represented by rapid short-tem voltage spikes that need to be discharged to ground.
FIG. 2A provides a circuit diagram for an example of how ESD events are handled by a typical RF coupler 102. As described above, an RF input signal is received at connection port 132 by the RF coupler 102 and is output as an RF output signal at connection port 134. As the RF signal passes through the RF coupler 102, coupling between the primary signal path and the secondary signal line generates the signals for the coupled port 136 and the isolated port 138, as described above. Inductive or magnetic coupling within the RF coupler 102 between the primary and secondary signal paths is represented by the inductor 202 and the inductor 204 within the dashed box 203 in FIG. 2A. Capacitive or electrical coupling within the RF coupler 102 between the primary and secondary signal paths is represented by capacitor 206 and capacitor 208, respectively. For a typical RF coupler 102, these capacitors 206 and 208 will break down when a voltage of about 200-400 volts is placed across them. As such, the ESD protection provided by a typical RF coupler 102 does not meet the 2 kV human body ESD model for static discharges. Thus, to meet this ESD protection at its connection points, the RF coupler 102 would need to be modified or enhanced to provide the necessary ESD protection.
FIG. 2B (Prior Art) provides a block diagram for ESD protection for a typical PA integrated circuit 104. Many integrated circuits will have ESD protection coupled to input/output pins for which ESD protection is desired. As depicted, PA integrated circuit (IC) 104 includes an output connection point 240 for the transmit signal line 110. On the integrated circuit itself, this signal line will be coupled to other internal circuitry, as represented by arrow 252, and would be coupled to PA ESD circuitry 250, if ESD protection were provided for this output connection point or pin. One example of ESD circuitry that is commonly used is a large diode connected between the signal line and ground. These diodes are configured to turn “on” when an ESD event occurs on the signal line so that a signal path is provided from the signal line to ground to discharge the ESD event without destroying the internal circuitry. As such, using this ESD circuitry, integrated circuits such as the PA integrated circuit 104 can meet the 2 kV human body ESD model for static discharges.
For many communication devices, reduction in the space and cost required for the power amplifier device and the RF coupler device is desirable. As such, it is desirable to reduce the size and cost required to implement the RF coupler and the PA integrated circuit while still meeting ESD protection requirements.